Certain natural stones, such as opal, have long been valued for the beautiful play-of-color they exhibit. These stones possess internal structures having a modulated index of refraction, absorption, or other optical parameter. The index of refraction or other optical parameter is modulated on the scale of wavelengths of visible radiation (i.e., light) and thus produces color by interference. This interference is wavelength and angle dependant so the stone appears to change color with the observer's viewpoint. Stones of this nature are commonly cut and polished to produce gemstones and other decorative articles. Examples of such stones include opal, fire obsidian, mother of pearl, and fire agate. Of these, opal is perhaps the most highly coveted.
There are three basic types of opal: (1) common opal; (2) fire opal, and; (3) precious opal. Common opal (i.e., potch) is the least valuable because it has no play-of-color. Common opal comes in white, grey, yellow, blue, green, and pink. Fire opal is named for its fiery red color. It ranges from a deep red to shades of orange and yellow. Fire opal is more valuable than common opal because of its coloring. Precious opal (i.e., gem opal) exhibits a coveted play-of-color and thus is quite valuable. Precious opal comes in a wide range of colors. Precious opals that are predominantly white or light blue are the most common, while those containing red, orange, or violet are more rare. Black opal (opal having a predominantly dark background) is the rarest and perhaps the most desired of the different types of opal.
All the different types of natural opal have the same chemical composition. Specifically, opal is characterized by silica having therein incorporated water molecules. Whether opal exhibits a play-of-color does not depend on there being any inclusion in the stone. Rather, this depends on the arrangement of silica spheres and water molecules. In cases where the silica spheres are of uniform size and arrangement (e.g., arranged in octahedrons), the light reflecting from them is split into spectral colors, and the stone appears to contain all the colors of the rainbow. In cases where the silica spheres are large or less uniformly arranged, the color range is minimal or non-existent.
Opal has been chemically duplicated in the laboratory. This opal is commonly referred to as synthetic opal. Synthetic opal is an artificially-made material that has the same composition and structure as its natural counterpart. A variety of methods are currently used to produce synthetic opal.
In addition to synthetic opal, attempts have been made to create simulated opals. Simulated opals are artificially-made materials that are similar in appearance to natural opal, but have different optical, physical, and/or chemical properties. One simulated opal type is known as Slocum Stone, a material produced years ago by an individual named John Slocum. The process used for making Slocum Stone was always kept secret. However, it is postulated that Slocum Stone was produced by a process similar to that used in producing dichroic glass beads and cabochons. For example, Slocum Stone specimens are known to contain air bubbles and randomly-oriented flecks of dichroic color, which are also characteristics of dichroic glass beads and cabochons.
Methods of making dichroic glass beads and cabochons (i.e., cabs) are known. Typically, these methods involve fusing together alternating sheets of dichroic-coated glass (i.e., glass bearing a dichroic coating) and uncoated glass. For example, dichroic-coated glass is commonly sandwiched between uncoated glass, and the resulting laminate is then fused in air (e.g., in a furnace) for several hours. During fusing, the dichroic film ruptures and curls. This rupturing is caused by sagging of the glass under the inflexible dichroic film. Because this rupturing is inherently random, a relatively small percentage of the resulting material is usable for gemstones. Moreover, a specific gemstone appearance cannot be consistently reproduced by this method due to the randomness of the film rupturing. Further, this process traps a significant amount of air between the glass sheets, leaving air bubbles in the resulting material. These bubbles diffract light in a gemstone formed from such material, creating murkiness and spots that detract from the appearance of the gemstone.
The processes used to produce Slocum Stone, dichroic glass beads and cabs, and various other materials are referenced below in Table 1. As noted above, the process used to produce Slocum Stone was always kept secret, and therefore the notes in Table 1 concerning Slocum Stone reflect the process the present inventors surmise was used to produce this material.
TABLE 1FormPrecipitateCoatFuse orPolymerizesilicasilica intodichroicsinter atplastic atFabricatemicro-pseudo-ontoCrushhighlowinto gemProcessspherescrystalImpregnationsubstratedichroictemperaturetemperature(lapidary)SlocumNoNoNoYesNoFuse in airNoYesStoneDichroicNoNoNoYesNoFuse in airNoNoglassbeadsand cabsImitationYesYesYes plasticNoNoNoYesYesopal(plasticbase)SyntheticYesYesYes silicaNoNoSinter in airNoYesopal(silicabase)SimulatedNoNomica inNoNoNoYesYesmother ofplasticpearlGoldstoneNoNocopper + carbonNoNoYes fuseNoYes
Numerous characteristics are considered to be desirable in a gemstone material. These characteristics include opal simulation, absence of air bubbles, color uniformity, color range, opalescence, color orientation, color layering, durability, and facetability. Regardless of the particular combination of these properties that is desired, low production cost is always preferred.
Various attempts have been made to produce synthetic and simulated gemstone materials that can achieve certain combinations of these characteristics. Unfortunately, no existing material has achieved all of these characteristics. Some existing materials are produced by complicated, expensive methods. For example, Slocum Stone and synthetic opal would be considered high cost materials. Those materials that are made by less complicated and/or costly methods tend to be limited in terms of their properties. This is borne out below in Table 2.
TABLE 2OpalAirColorBaseColorColorMaterialCostDurabilitysimulationbubblesuniformitycolorFacetableOpalescenceOrientationlayeringSlocumHighGoodFair-GoodSome-PoorNoneNoNoYesNoStoneManyDichroicLow-GoodFair-GoodManyPoorAnyNoNoYesNoglassModeratebeadsand cabsImitationLowPoorNear-NoneExcellentPastelYesYesYesYesopalPerfectto(plasticBlackbase)SyntheticHighVeryNear-NoneExcellentPastelYesYesYesYesopalGoodPerfectto(silicaBlackbase)SimulatedLowPoorPoor-FairNone-GoodPastelNoYesYes or NoNomother ofFewtopearlBlackGoldstoneModerateGoodNotSomeExcellentSeveralNoNoNoNoApplicable
It would be desirable to produce a gemstone material that resembles opal or another natural gemstone. For example, it would be desirable to produce a gemstone material having therein embedded dichroic particles. It would be particularly desirable to provide such a gemstone material wherein the dichroic particles are substantially uniformly oriented. It would also be particularly desirable to provide such a gemstone material wherein the dichroic particles are present in a certain size distribution. Further, it would be particularly desirable to provide a gemstone material that comprises dichroic particles and is substantially free of air bubbles. Still further, it would be desirable to provide a gemstone material that can achieve any combination of desirable gemstone characteristics. It would be particularly desirable to provide a gemstone material of this nature that can be produced at low cost.